| Graphene quantum dots(GQD)are quasi-zero-dimensional nanomaterials with a graphene structure,which inherit the excellent characteristics of graphene such as good electron mobility.And it has a significant quantum confinement effect,which makes up for the defect of graphene's insufficient band gap.It is a material with stable optical properties.These unique physical and chemical properties make GQD have a wide range of application prospects in the fields of photocatalysis,electrocatalysis and energy conversion.The small size of GQD also severely restricts the preparation methods of its composite materials.Most traditional preparation methods focus on introducing GQD into the host material,or using GQD as a carrier to support active species to maximize the performance of composite materials.However,there are still few reports on the design of new structures based on GQD and the research on novel preparation strategies.In view of this,this article starts from the design of new GQD-based nanostructures,and proposes a synthesis strategy based on supramolecular assembly to prepare GQD supramolecular assemblies with two-dimensional structures.We explore the factors that influence the structure of the assembly and study the assembly mechanism.Furthermore,GQD/metal oxide derived from the assembly is applied to electrocatalytic oxygen evolution reaction,and GQD/metal phosphide is applied to solar-driven seawater desalination.The specific research content is as follows:(1)We use the top-down method to oxidize carbon black to obtain GQD with specific functional groups.Through XPS and FTIR analysis,we determined that there are a large number of carboxyl groups on the surface of GQD.Then,it is mixed with copper acetate solution in an appropriate ratio and freeze-dried to obtain supramolecular assembly.It can be observed by SEM that when the mass ratio of GQD:Copper salt is 10:3,the assembly is a nanosheet structure with a smooth surface.This is a very novel structure based on GQD assembly.By changing the types of functional groups on GQD,1,3,6-trinitropyrene is used to synthesize GQD with hydroxyl and amino groups as the main functional groups from the bottom up.And when the same proportion of copper acetate was added,it was found that no nano-sheet-like structure was formed,which verified that the type of functional group in GQD would affect the structure of the assembly.Finally,we further studied the assembly of other types of acetate(such as cobalt acetate,nickel acetate,and iron acetate)with GQD,and all obtained nanosheet structures.Therefore,we proposed a universal synthesis strategy based on GQD assembly(2)The Co,Fe and Ni precursors obtained in the above experiment were calcined at high temperature to obtain the corresponding metal oxide and GQD composite materials GQD/CoO,GQD/Fe2O3 and GQD/NiO.Characterized by SEM and TEM,the GQD/metal oxide composite still has a two-dimensional sheet structure,but the surface becomes rough,and a nano-cluster structure is formed during the high-temperature calcination process.When three kinds of GQD/metal oxide composite materials are used as OER catalysts,GQD/CoO,GQD/NiO and GQD/Fe2O3 reach current densities of 50 mA cm-2 at overpotentials of 360 mV,420 mV and 460 mV,respectively.Among them,GQD/CoO has the best OER activity.This aspect is attributed to the fact that the nanoclusters in the two-dimensional sheet structure can greatly increase the number of active sites.The good electron mobility of GQD promotes the charge transport in the catalytic reaction.At the same time,a continuous mass transfer path is also formed in the two-dimensional sheet structure.The excellent performance of GQD/metal oxide composites derived from GQD supramolecular assemblies in electrocatalysis was verified.(3)GQD/Cu3P composites were prepared by low-temperature phosphating on the GQD/Cu2+ assembly.Experiments have found that the surface of the Composite material is hydrophobic and maintains a two-dimensional sheet structure.The material is applied to photothermal seawater desalination,that is,under the irradiation of a strong sunlight,the interface temperature can reach 51? in a short time,and its evaporation rate and photothermal conversion efficiency are 2.34 Kg m-2 h-1 and 94%.Compared with other photothermal materials based on carbon structure and containing metal species,the performance is very outstanding.In addition,the composite material has good stability and salt rejection.The effect of the proportion of Cu3P in the composite material on the performance was further optimized,and it was confirmed that the excellent performance of the composite material comes from the synergistic effect of GQD and Cu3P.The thickness of the material is further optimized,and the optimal performance is obtained when the thickness is 2 mm.If the material is too thick or too thin,it will cause heat loss and affect the performance of seawater desalination. |
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